Electron beam influencing apparatus



March 8, 1949. o sc ELECTRON BEAM INFLUENCING APPARATUS 5 Sheets-Sheet 1 Filed Feb. 19, 1947 Q INVENTOR OTTO H. SCHADE AHORNEY March 8, 1949. Q E 2,463,720

ELECTRON BEAM INFLUENCING APPARATUS Filed Feb. 19,1947 5 Sheets-Sheet 2 INVENTOR OTTO H. .iCADE BY 7Y7 W ATTORNEY March 8, 1949. o. H. SCHADE ELECTRON BEAM INFLUENCING APPARATUS 5 Sheets-Sheet 5 Filed Feb. 19, 1947 Fi .4 W

QES

INVENTOR OTTO H SCHADE BY 5W ATTORNEY March 8, 1949. O. SCHADE ELECTRON BEAM INFLUENCING APPARATUS 5 Sheets-Sheet 4 Filed Feb. 19, 1947 v INVENTOR. OTTO. SCHADE IATTORN EY a h 8, 1949. o. H. SCHADE ELECTRON BEAM INFLUENCING APPARATUS 5 SheetsSheet 5 Filed Feb. 19, 1947 .i l lllllllllll h| lllll l I l l IIH lNVENTOR. OTTO H. SCH/10E ATTORN EY Patented Mar. 8, 1949 ELECTRON BEAM INFLUENCING APPARATUS Otto H. Schade, West Caldwell, N. l, assignor to Radio Corporation of America, a corporation of Delaware Application February 19, 1947, Serial No. 729,422 11 Claims. (Cl. 250-457) My invention in general relates to devices and apparatus for focussing and deflecting an electron beam, and more particularly to such apparatus as is especially adaptable for use in focussing and deflecting the cathode ray beam in the so-called low Velocity beam scanning cathode ray image pick up or camera tubes, such as those known as the orthicon and/or image orthicon, for instance.

In the television art an optical image to be transmitted is focussed onto a photosensitive mosaic target element of the camera tube to release electrons therefrom, and the quantity of released electrons from each point on the mosaic is representative of the light intensity of that point of the optica1 image being scanned and which impinges thereon. A cathode ray beam then is moved according to any desired scanning pattern, e. g., in a line by line manner, over the mosaic and signals are accordingly developed sequentially point by point either by the measurement of the changes in the total charge on the mosaic as the beam traverses it or by the measurement of the effect of the mosaic charge on the cathode ray beam itself.

In the earlier arrangements of the art to which this invention belongs, it was normal procedure to develop a beam of electrons and to accelerate the speed of the electrons in the beam toward the mosaic to a degree Where the electrons, when striking the photosensitive mosaic, struck at a high rate of speed and substantially neutralized the charge on the mosaic. The speed of the electrons upon striking the mosaic was sufficiently great, however, to release secondary electrons from the mosaic and, in some systems, video signals were derived by a collection of the secondary electrons so released. This beam then could be called a so-called hard beam or a stiff beam where the electrons passed through the deflection fields at a relatively high speed. The arrangements suffered from the disadvantage that the efficiency of the scanning tube was not as high as could be desired. Further, there was a tendency on the part of the scansion tube to produce background shading or spurious effects that were not found in the scene being televised, the latter apparently being due to the fact that the speed of the electrons in the beam being great enough to dislodge secondary electrons, these latter electrons, once having been freed, could be attracted to a collector ring or could be attracted back to the positively charged portions of the photosensitive mosaic and thus, by neutralizing at least a portion of the positive charge, alter the charge distribution from its original or true form so that a shading effect was produced.

There was developed, in the later art, a scansion tube that retained some of the features of the earlier form of camera tube but which had much greater efficiency. This was the so-called orthicon type of tube and such a tube is shown, for instance, in an article entitled The orthicon-A television pick up tube by Rose and Iams, published in the RCA Review for October 1939. Another article by the same authors is Television pick up tubes using low velocity electron beam scanning, Proc. I. R. E., September 1939. This tube avoids the release of secondary electrons from the photosensitive mosaic due to the action of the electron beam by changing from a high velocity scanning beam to a low velocity scanning beam. A further development of the tube led to the invention of the so-called Image Orthicon tube, and such a tube is shown, for instance, in the article by Rose, Weimer, and Law, entitled The image orthicon, Proceedings 1'. R. E. and Waves and Electrons, July 1946, pages 424 et seq.

The "image orthicon such as is used at present (one example of which is manufactured by RCA and identified as the RCA2P23) is very stable in performance at all light levels from several thousand foot-candles to one foot-candle, or less, and has a sensitivity which is in the order of times that of previous pick-up or camera tubes.

The image section of the image orthicon type tube, for instance, contains, among other elements, a semi-transparent photocathode on the inside of the tube end wall, an accelerator electrode, and a target which consists of a thin glass disc with a fine mesh screen very closely spaced to it on the photocathode side. Focussing in image section is accomplished by means of a magnetic field produced by external coils and by varying the photocathode voltage.

Light from the scene being televised is picked up by an optical lens system and focussed onto the photocathode which emits photoelectrons from each illuminated area in proportion to the intensity of the light striking the area. The photoelectrons released upon the light image being iocussed upon the photosensitive cathode are focussed on the target by means of developed magnetic fields which function in conjunction with the tube. Electrostatic accelerating fields move the electrons between the photoelectric cathode and the target disc and provide the initial focussing effect.

On striking the target, the released electrons cause secondary electrons to be emitted from the glass target face. The secondary electrons thus emitted are collected by the adjacent mesh screen which is held at a definite potential of about one or several volts relative to the photocathode area. The maximum potential to which the glass disc may rise is therefore limited for all values of light and stable operation is achieved. Emission of the secondary electrons leaves, on the photocathode side of the glass target, a pattern of positive charges which are representative of the values of light and shade at homologous areas of the scene being televised. The charges thus produced set up a corresponding potential pattern on the opposite, or scanned side, of the glass target.

The opposite side of the glass target from that on which the charges are formed is scanned by a low velocity electron beam produced by the electron sun of the tube. The beam is iocussed at the target by a magnetic field produced by focussing coils positioned externally to the tube, as well as by the electrostatic field produced due to voltage differences between certain electrodes within the tube.

There is further provided in the tube 21 dec crating electrode to create a field for decelerating the electrons of the electron beam just prior to their approach to the target. The electrons stop their forward motion at the surface of the glass target. Those electrons not required to neutralize the charges in the target are then influenced by the fields within the tube and are caused to turn back toward the source and then are collected and focussed onto a multi-stage electron multiplier, except when the beam approaches the positively charged portions of the pattern on the glass target. When the latter condition occurs, the electrons are deposited from the scanning beam or absorbed from the scanning beam in quantities sufficient to neutralize the charge pattern on the glass and this absorptively modulated beam is directed back to the multiplier. This deposition or absorption leaves the glass with a negative charge pattern on one side corresponding to the positive charge pattern on the other side. These charges neutralize each other by conductivity through the glass in a time that is less than the scanning time of a frame of the picture transmission.

While this particular type of tube is highly desirable because of its efiiciency and sensitivity, it also brings about difficulties that are not present when the high velocity beam type of tube (e. g., the ico-noscope) is used, and these difficulties are present because the low velocity electrons in the electron scanning beam are diflicult to focus and control.

For one thing, the electron velocity being comparatively low, a relatively weak electrostatic or electromagnetic field will affect the beam. Consequently, stray fields have an effect on the beam which must be eliminated and it is one of the objects of this invention to provide means for focussing and deflecting a cathode ray beam which will be particularly useful for use with low beam velocity scanning tubes, but not necessarily limited thereto, and in which the efiects of stray fields from sources external to the tube will be minimized or eliminated.

Another effect which presents difliculties and which should be eliminated or minimized to the degree where it constitutes no problem is the effect of undesired magnetic fields in the image or target section of the tube with which the apparatus is used. The deflecting coils present a varying magnetic field and, in addition, to the field between the halve of the coils and which is desired to influence the deflection of the oathode ray beam, there is a large component of fringe flux emanating around the ends of the coils and this can severely limit the operating efficiency of the tube. It is a major object of this invention, therefore, to provide an apparatus in which fringe flux from the deflecting coils and the action of stray magnetic fields from sources outside of the apparatus will be minimized or eliminated.

Other and further objects of my invention will be apparent from a reading of the hereinafter appended specification.

My invention, in general, contemplates the provision of an insulating cylinder focussing coil form about which the focussing coils are wound in separate sections which are independently energizable. About the focussing coil is wound, in one embodiment of my invention, a succession of layers of audio steel strips separated apart by a fish paper wrapping. In another embodiment of my invention, there is placed about the entire focussing coil structure an iron cover which acts as a magnetic shield at the outer surface of the device and which, with other elements of the invention, forms a return path for the fringe flux from the deflecting coils which has a very low reluctance. Between the focussing coils and the insulating cylinder there is provided a special form of electrostatic shield which is described more particularly in the U. S. patent application Serial No. 729,421 of Schade and Goodale filed February 19, 1947 and entitled Electron beam control apparatus.

There is provided a second insulating cylin- "T der which acts as a support for the horizontal and vertical deflecting coils of the apparatus. The coils are mutually separated from each other by an insulating wrapping and by an electrostatic shield of the type shown in the application of Schade et al., hereinbefore mentioned. Additionally, there is provided a similar electrostatic shield interposed between the deflecting coils and the insulating support member. This subject matter has been thoroughly explained in the Schade et a1. application and will not be explained in detail in the present application.

The inner diameter of the insulating cylinder supporting the focussing coils is such that the deflecting coil assembly can be slid into the cylinder so that the deflecting coils are interposed between the focussing coils and the cathode ray tube with which this apparatus is associated.

The alignment coil is contained in the space between two copper cylinders and is constructed so that it may be slipped over the insulating support for the deflecting coils and is held in a position between the focussing coils and this insulating support.

When the image orthicon type of scansion tube is used with this apparatus, there is provided an additional focussing coil which is supported by a cylindrically shaped support which may be slipped into the focussing coil supporting cylinder and is arranged to abut against and fasten to the deflecting coil assembly.

Near one end of the support for the additional focussing coil is positioned a tube socket on the inside of an insulating holder which is slipped into the assembly and the neck of the tube may be passed through the assembly and the body of the tube seated against the tube socket.

Interposed between two of the sections of the focussing coils is one or more annular ring-like members and at the end of the deflecting coil assembly there is a second similar annular memher which is positioned substantially coplanarly with the first annular member. These two annular members are made of Mumetal or A metal or may be made of other highly magnetic material. There may be positioned between the second of these annular members and the body or target containing section of the scansion tube one or more additional annular members made of highly permeable magnetic material. Additionally, another of the same type of highly permeable members may be positioned so as to embrace the lower end of the body section of the cathode ray tube. The annular members and the audio steel strips or the iron cover around the apparatus then form a very low reluctance magnetic path between the end of the deflecting coils and the outside of the assembly. In

actual practice, this has multiplied the operating efiiciency of the tube in terms of scansion lines by several times.

Similarly, at the opposing end of the deflecting coils, there may be provided one or more annular rings of Mumetal or A metal or other highly permeable material and, in actual operation, these will be positioned between the electron multiplier section of the scansion tube and the end of the deflecting coil, the purpose being to cut down or eliminate any effect that the fringe flux from the coils might have on the multiplier section. Positioned substantially coplanarly with such rings would be another set of Mumetal or A metal rings normally positioned between two of the sections of the normal focussing coil arrangement and running up to the iron sheath surrounding the entire assembly or, where audio steel strips are used, the rings would run substantially to the outer surface of the assembly. The provision of these members has actually increased the operating efiiciency of the tube in terms of scansion lines by a considerable amount.

My invention will best be understood by reference to the drawings in which Fig. l is a view partially in cross-section of a focussing and deflecting apparatus embodying my invention;

Fig. 2 is an exploded perspective showing of the different portions comprising the deflecting and focussing assembly in accordance with my invention;

Fig. 3 is a perspective view of an end of the assembly showing supporting apparatus for an electron beam tube and driving apparatus for moving parts of the device relatively to each other;

Fig. 4 is a schematic showing in cross-section of a portion of the apparatus to illustrate the principles of the invention;

Fig. 5 is a showing of one form of magnetic shield arrangement;

Fig. 6 is a schematic showing in cross-section of a portion of the apparatus to illustrate the principles of the invention; and,

Figs. 7 and 8 are schematic showings of the additional focussing coil and the mount therefor.

Referring to Fig. 1, there is shown a partial cross-sectional view of the focussing and deflecting apparatus for use with cathode ray tubes and which is particularly adaptable for use with the so-called image orthicon type of cathode ray scansion tube. The image orthicon, in principle, has been described hereinbefore in this specification and there has been described the fact that the tube has one beam moving at a low velocity toward the target area upon which it is focussed and that, after the bending of this beam away from the target area, it is returned at low velocity and focussed, in one type of such tube, onto an electron multiplier.

In the illustrated arrangement of the figure, there has been provided a hollow cylindrical insulating support member In for supporting the focussing coils. At each end of the cylinder there are provided annular co-acting clamping members H and i2. Wound about the member I0 is a special form of electrostatic shield l3 which is held firmly clamped at its edges by the members H and i2. This shield forms a portion of the subject matter of the Schade et al. application hereinbefore referred to and reference may be had thereto for an extended description thereof.

The normal focussing coil sections l5, l6 and I! are placed about the cylinder Ill. The sections I5 and 15 are separated from each other by annular insulating ring-like members [8 and I9 which contain between themselves an annular member I8 comprised of Mumetal or A metal or other highly permeable magnetic material. Sections ['5 and ll of the focussing coils are spaced apart by annular insulating member 2|. In the space between the clamp members l2, l2 there is a succession of layers comprising audio steel strips 2! separated by waxed twine and 1 having each layer appropriately separated by insulating fish paper, and the entire assembly is wound with a cover of acetate cloth .electrical tape. Energizing leads for the coil sections may be brought up through the layers at the top of the focussing coil and out through the acetate wrapping.

A second insulating hollow cylinder 40 is provided which acts as a support for the deflecting coils and the alignment coil structure. Wound about the cylinder 40 is a special type of electrostatic shield of the type explained in the Schade et a1. application hereinbefore referred to and this shield is held firmly in place by the clamping members 45, 48 and 49, 50. The horizontal deflecting coils are then positioned about the cylinder 40 with the shield 42 interposed between the cylinder and the coils 43.

Wound about the horizontal deflecting coils is a layer of fish paper wrapping and on top of the latter layer there is positioned another of the hereinbefore referred to special type of electrostatic shield which is held at its edges by clamping members such as 46 and 49.

A further layer of fish paper wrapping is provided and the vertical deflecting coils (which are shown partially in cross-section) are positioned about the latter fish paper wrapping. The short energizing leads of the coils are brought out through holes drilled through the shell of a cylindrical member to a terminal strip 66 where they are fastened to terminals 61. The deflecting coils per so do not form the subject matter of this invention and, accordingly, well known forms thereof may be used such, for instance, as shown in Tolson U. S. Patents Nos. 2,155,514 granted April 25, 1939 and 2,167,379 granted July 25, 1939.

llhe alignment coil i0 is contained in the space between two copper cylinders H and '12 and the space between them is joined at the edges by two .annular copper rings so that the appearance of the alignment coil is that of a thick copper cylinder. This construction is important as brought out in the Schade et al. application Serial No. 729,421, supra. Energizing leads may be brought through the wall of the annular copper ring to a. tirminal strip which contains terminals such as I When the image orthicon type of tube is used, there is provided an additional focussing coil. This coil is wound in the space between two annular members BI and 82 which form a part of the cylindrical member 30. Suitable spacers 8| are provided and the coil 83 is wound in the space between them. The diameter of the cyl inder 80 is such that it may be slipped into the iocussing coil insulating support cylinder I and abuts against and may be fastened to the end of the deflecting coil assembly.

Near the end of the cylinder 80 which abuts against the deflecting coil assembly there is p-rovided an annular member 85. On the inside of the cylinder and positioned between the member 851 and the end of the cylinder 86 is a Mumetal or A metal or other highly magnetic material annular member 84. The position of the member 84 is such that normally it is arranged to be in a substantially coplanar relationship with the annular member 26 positioned between insulating rings I8 and I9 and which has a very low magnetic reluctance.

A third insulating support cylinder 95 is provided which ends in an annular flange-like member SI and the outer diameter of this cylinder is such that it may be slid into the cylinder 89 and the annular member 9I will abut against the annular member SI of cylinder 80. Near the end of the cylinder 9D, remote from annular member 9| and positioned inside of the cylinder, is an insulating tube socket member 92 and the body or target section of the scansion tube abuts against the socket 912 and leads or pins of the tube fit in the socket holes. Energizing potentials may be furnished to the tube by means of copper strips 93 running from terminals 94 against the inner surface of the cylinder 90 to the socket holes in the member 92.

Positioned against the tube holder 92 and on the side thereof which is adjacent the target section of the tube in its operating position is a further annular member 95 which is of Mumetal or A metal or other material having a very low magnetic reluctance.

Referring to Fig. 2, there is shown an exploded view of the apparatus embodying my invention to show the relative positioning of the various parts of the device. This View is for purposes of illustrating principles only and no attempt has been made to maintain scale relations since the relative size of the elements will depend upon the particular tube with which the apparatus will be used. In this view, the outside wrapping 39 of the focussing coil is shown and the coil is illustrated as being contained between two aluminum end plates Iifl and Ill. The cylinder 80 having the annular members 8i and 82 is illustrated with the additional focussin coil 33 wound between the two annular members. The cylinder 80 will be inserted into the opening furnished by the cylinder II) about which the focussing coil is wound and the annular member 82 will abut against end plate Hi3. Mumetal or A metal ring 84 will abut against the structure fastened to the end of the deflecting coil assembly on the inside of the focussing coil cylinder.

The insulating cylinder 90 containing the tube socket is inserted in the opening of cylinder until annular member 9| abuts against annular member 8|. The copper strips 93 with the terminals 94 are illustrated and shown as following the inner surface of the cylinder 90.

The insulating cylinder 40 about which the deflecting coils are positioned is shown partially inserted in the opening of the focussing coil support cylinder and this assembly will be slipped into the focussing coil assembly until the annular member about member 65 abuts against the end plate Ill.

The alignment coil contained between the two copper cylinders II and I2 will be slipped over the insulating cylinder 40 and up into the structure until it abuts against member 65 on the inside of the deflecting coil assembly.

A bracket member having side plates I I5, H6 and end plate II! will be brought up into position so that the edges of the side plates may be fastened by screws or other appropriate means to the end plate Ill. The tube neck will be seated in the circular structure I I8, and the latter may be moved by turning gear I20 which meshes with the gear segment I I9.

Gear I2I will mesh with the gear segment on the alignment coil and the alignment coil may be rotated by turning the shaft joined to the Similarly, the deflecting coil structure may be rotated by turning the shaft of gear I22, which, in position, meshes with the gear segment on t e focussing coil assembly.

Referring to Fig. 3, there is shown a perspective view illustrating the relative positioning between the bracket member and the end plate I II on the focussing coil structure. The circular yoke 8 which forms a part of member II'I has, on the inside thereof, a thin bronze spring winding in which the tube neck is seated and this may be tightened by the action of the screw member which passes through the structure.

The relative positioning of the gear segment on the alignment coil and gear I2I is shown and the relative positioning of the gear segment on the deflecting coil assembly and the gear I22 is shown.

Referring to Fig. 4, there is shown a partial view in cross-section of a modified arrangement in accordance with my invention. In this view, the insulating cylinder II] is illustrated with the annular end ring I2 shown. The Mumetal annular member 20 is shown and one of the sections I 5 of the focussing coil is contained between members I2 and Eli. A portion of the focussing coil section I B is illustrated and also there is shown the relative positioning of special electrostatic shield I3 which would be constructed in accordance with the teachings of the Schade et a1. application hereinbefore referred to.

A portion of the horizontal deflecting coils 43 is shown and the vertical deflecting coils 60 is shown, as well as special electrostatic shields 42 and 56. No attempt has been made to show the manner of clamping the special electrostatic shields since this has been clearly illustrated in Fig. 1. Nor has the additional focussing coil specifically been illustrated such as is used with the image crthicon and which is shown in Fig. 1, the purpose of this view being to show the manner in which the eifect of the fringe flux from the deflecting coils is minimized or eliminated.

A Mumetal or A metal or other highly permeable material annular member 84 is illustrated positioned in a substantially coplanar relationship with respect to the annular member 20. Between the body or target containing section of the tube and member 84 is a second annular Mumetal ring 95 which hasbeen illustrated as fastened to the member 84. Still a third annular highly permeable ring I30 is illustrated and this has been shown as held by member 95. It will be appreciated that this is for the purpose of illustrating principles and need not be the exact manner in which the structures are maintained relatively spaced apart from each other. The latter highly permeable ring I30 is positioned very near the inner face of the target containing section of the scansion tube and embracing this section of the tube, the tube itself being shown in dotted lines.

About the entire structure there is placed an iron cylinder I35 and this takes the place of the audio steel strips illustrated in Fig. 1. It will be appreciated that both structures could be used, if desired, the purpose being to provide a very low reluctance return magnetic path for the fringe flux from around the edges of the deflecting coils and by means of which it is led to the outside of the entire structure.

Referring to Fig. 5, there is shown one arrangement of several of the Mumetal or A metal members such, for instance, as the members 95 and I30 of Fig. 4. The member 95 may be an annular member having an aperture therein which is sufficiently great to allow the neck of the tube with which the apparatus is to be used to be passed therethrough and the member I30 may have an opening therein which is sufficiently large so as to accommodate the passage therethrough of a portion of the body section of the tube. In accordance with the illustration of Fig. 4, it will be seen that this latter member embraces the body portion of the tube at a section thereof which is between the end of the deflecting coils and the target in the tube. These annular rings could be held together by conducting pins, such as illustrated, or by other well known means.

Referring to Fig. 6, there is shown in crosssection a schematic illustration of an arrangement by means of which the efiect of the fringe flux emanating from the end of the deflecting coils adjacent the electron multiplier section of the scansion tube may be minimized or eliminated. In this view, the alignment coil II! has been shown and the relative positioning thereto of the insulating cylinder 40 about which the deflecting coils are placed. The horizontal deflecting coils 43 and the vertical deflecting coils 80 have been partially shown, as well as the insulating cylinder I about which the focussing coils are placed. Sections I6 and II of the focussing coils are shown, and, in this illustration, the iron sheath I35 surrounding the assembly also has been illustrated. A portion of the scansion tube has been shown by dotted lines.

In this arrangement, there is provided at the end of the vertical and horizontal deflecting coils a pair of insulating spacer members I48 and MI and positioned between the spacers is a Mumetal or A metal annular member I42. Positioned substantially coplanarly with the member I42 is an additional Mumetal or A metal annular member I43 which, in this illustration, has been shown as being interposed between two sections it and I! of the focussing coil assembly. There are also provided two insulating spacer rings I44 and I45, one of each being positioned on each side of the member I43. This is similar to the arrangement of the spacer rings I8 and I9 and the Mumetal ring 20 of Fig. 1.

It will be noted that the rings I42 and I43 will,

with the iron sheath member I35, provide a very low reluctance return path for fringe flux emanating from the ends of the coils of the deflecting coil assembly. This arrangement is necessary because otherwise the fringe flux could affect the operation of the electron multiplier I56 by upsetting the focus of the beam which has been modulated by the signals on the photosensitive member of the scansion tube and which has been turned and, in operation, is directed toward and focussed onto the electron multiplier input. In actual operation, this has contributed extensively to the number of scansion lines of good detail which can be developed by the tube as compared with the number of scansion lines of the same detail which could be developed without the use of this arrangement.

The structure hereinbefore set out constitutes an arrangement which has allowed efficient scanning of a number of lines that is several times as great as was possible where this arrangement has not been used. Previously, it was attempted to eliminate the fringe flux effect by the use of an additional coil which was so energized that its flux would buck out the fringe flux from the deflecting coils or a copper sheet which was used as an eddy current sheet. These did not prove satisfactory, the arrangement of a low reluctance path giving results which were definitely superior to those where the bucking coil is used.

The purpose of the audio steel strips or the iron cylinder with its associated Mumetal rings has been several fold. The arrangement provides a low reluctance return path of the magnetic field from the deflection coil coming out of the coil window or pole on one side to the opposite side of the coil assembly and back to the opposite pole, thus preventing spreading of this field into space and through the target containing section of the cathode ray tube with which the device is used with its consequent undesired effects. The fringe field from the coil front is, so to say, sucked up by the annular metal highly permeable partitions and returned in the shortest possible way back to the steel strips or iron cover and from there into the coil, thus reducing considerably the stray field from the front opening of the deflection coils. Both the annular partitions and the associated iron cover are therefore very effective in constrainingthe deflection field to the back or neck section of the cathode ray tube where it is desired and in preventing pick-up of spurious signals induced by the deflection fringe fields in the signal output lead or leads leading to the multiplier element.

A second effect of the highly permeable shield arrangement is to increase the efiiciency of the deflection coils, and a third effect is to minimize the influence of external stray fields from other sources on the action of the cathode ray tube used with the apparatus.

Referring to Fig. '7, there is shown one arrangement which has been used as the additional focussin coil structure. The structure may be formed of a cylindrical metallic member which has at one end thereof a flange-like annular member and at a position intermediate the other end thereof a second annular ring embracing the outer periphery of the cylinder. focussing coil is wound in the space between these two annular members. The surface of the cylin- The additional cylinder and these windows continue to a position near the end of the cylinder. In one embodiment of this arrangement, the surface of the cylinder is cut away so that two relatively narrow conducting strips, one of which is shown as the strip I50, extend from the neighborhood of the annular rin 82 to a position near the end of the cylinder and this leaves the end in the form of a ring of conducting material Hill. In this end section, the annular ring 85 of Fig. 1 is provided against which the Mumetal ring 84 of that figure rests. The windows in the surface of the cylinder all then may be filled by an insulating material such as Bakelite or other well known materials so as to give rigidity to the structure.

Referring to Fig. 8, there is shown an alternative form of the additional focussing coil support and one which has been very effective in practice. In some respects this may be described as a modification of the arrangement shown in Fig. 7 Instead of having the windows of the structure of Fig. '7 filled with Bakelite or other insulating material, the sections, which in Fig. '7 are the window sections, comprise, in this arrangement, a series of conducting strips which are cut from the surface of the cylinder itself and these conducting strips are shown, for example, by the strips I55, I55 and so forth. The end ring l! of the cylinder has riveted thereto a Bakelite insulating ring I (it to which the ends of the strips I,

such as I55 and I56 are riveted in order to keep these strips firmly in place. This provides a structure in which there are a minimum of conducting paths for the circulation of eddy currents in the structure which would be set up by coupling from the front of the deflecting yoke and which could affect the photosensitive mosaic in the tube with which the apparatus is used. This type of structure has increased by a great number of lines the number of scanning lines that it is possible to develop with the tube used with the structure and where such lines have acceptable resolution. This structure provides, however, a good ground connection from the outer frame of the apparatus, as for instance the members Ill] and I l I, to clampin members 45 and 45 which clamp one of the electrostatic shields and the unnumbered clamping member cooperating with the member 46 and clamping the other electrostatic shield.

It will be appreciated that, if desired, the strip members I55 and I56, for instance, need not all emanate from the section of the cylindrical support 80 which is in the neighborhood of the annular member 82, but could be arranged so that alternate members emanate from the front ring l5! of the structure so that effectively there would be provided a set of strip-like or finger-like members which are interleaved.

Having now described the invention, what is claimed and desired to be secured by Letters Patent is the following.

What I claim is:

1. In apparatus for deflecting and focussing an electron beam, means for deflecting said beam in at least one coordinate of its movement, magnetically permeable means positioned adjacent said deflecting means, means for focussing the beam, and magnetically permeable means positioned adjacent said focussing means and in the neighborhood of the magnetically permeable means positioned adjacent the deflecting means.

2. Apparatus in accordance with claim 1 wherein the magnetically permeable means adjacent the deflecting means and the magnetically per- 12 meable means adjacent the focussin means comprise annular members positioned substantially coplanarly.

3. Apparatus in accordance with claim 1 wherein there is provided, in addition, magnetically permeable means at least partially embracing the deflecting means and the focussing means.

4. In apparatus for influencing an electron beam, means for deflecting said beam, magnetically'permeable means positioned adjacent the beam deflecting means and intercepting at least a part of the fringe flux emanating from the deflecting means, beam focussing means, magnetically permeable means positioned in the neighborhood of said beam focussing means, and magnetically permeable means at least partially embracing the deflecting and focussing means, said. magnetically permeable means forming a low reluctance magnetic path for the fringe flux from said deflecting means from the region adjacent the end of the deflecting means to a region exterior to the focussing and deflecting means.

5. In apparatus for influencing an electron beam formed within a cathode ray tube which has a section containing a target area toward which the beam is directed, means for deflecting said beam, annular magnetically permeable means positioned between the deflecting means and the target containing section of the tube, electron beam focussing means, an annular magnetically permeable means positioned in the neighborhood of the electron beam focussing means, and magnetically permeable means at least a portion of which at least partially embraces the deflecting means.

6. Apparatus in accordance with claim 5 wherein the magnetically permeable annular means positioned between the deflecting means and the target containing section of the cathode ray tube and the magnetically permeable means positioned in the neighborhood of the electron beam focussing means are positioned in a substantially coplanar relationship.

'7. Apparatus in accordance with claim 5 wherein there is provided in addition a second annular magnetically permeable means positioned in the neighborhood of the magnetically permeable means which is located between the deflecting means and the target containing area of the tube.

8. Apparatus in accordance with claim 5 wherein the magnetically permeable means least partially embracing the deflecting means comprises an iron sheath.

9. Apparatus in accordance with claim 5 wherein the magnetically permeable means least partially embracing the deflecting means comprises a plurality of audio steel strips.

10. In apparatus for influencing an electron beam developed within a cathode ray tube having a section thereof containing a target toward which the electron beam is directed, means for deflecting the beam in at least one coordinate of movement, magnetically permeable means positioned adjacent the end of said deflecting means and interposed between the deflecting means and the target containing section of the tube, and a second magnetically permeable means positioned adjacent the first magnetically per-- meable means and at least partially embracing the target containing section of the tube when the tube is located in cooperative relationship with the beam influencing apparatus.

11. Apparatus in accordance with claim 10 bracing the beam deflecting apparatus.

OTTO H. SCI-IADE.

REFERENCES CITED The following references are of record in the file of this patent:

Number UNITED STATES PATENTS Name Date Farnsworth July 6, 1937 Tolson July 25, 1939 Schlesinger Jan. 30, 1940 Hepp Oct. 8, 1940 

